Control what you can. Let go of the rest.

Kelly spent a record 340 consecutive days in space aboard the International Space Station, starting March 27, 2015 and ending March 1, 2016. Most of that time was spent conducting experiments and taking some absolutely astounding photos of our big, blue planet … and beyond. But in July 2015, the ordinary quickly became life-threateningly extraordinary.

On July 16, 2015, Kelly and his Russian colleagues on the ISS were forced to hunker down in the Soyuz capsule as fragments from an old Russian weather satellite whipped past the space station at 17,500 miles per hour. The fragments of space junk missed the Space Station by one and a half miles — by the skin of our teeth, in celestial terms. But it was still close enough to leave an impact on Kelly and his crew.

During a keynote address with his twin brother Mark at the 2016 ASAE Annual Meeting in Salt Lake City, Kelly recounted the incident in hair-raising detail — including the part when the crew realized that, because the satellite’s debris was traveling at about 20 times the speed of a bullet, they would never know if a collision had taken place.

“There were two possibilities,” Kelly told the ASAE crowd. “It either misses us, or we’re vaporized. If it had hit us, we never would have known.”

At that moment, Kelly said, “there’s so much happening that we had no control over. The key is to focus on what you can control.”

For Kelly, that meant that NASA was handling the really hard stuff. His job was to nail down the things for which he was responsible. Were all the hatches locked down tight? Were his crew hunkered down where they needed to be? Was he mentally reviewing the checklists that would ensure the safety of his crew?

“Pay attention to the details, no matter how small,” Kelly told the ASAE crowd. “The unlikely things often are the ones that have the biggest consequences.”

In other words, quit worrying about the things you can’t control — your competition, for instance, or your regulators’ reactions, or how the markets will react.